Seedstocks of green snail may be transported as adult shells collected from the field. This method is straightforward and easy to implement if appropriate wildstocks were available.
Transportation of adult green snails may be practiced after that of trochus (Asano, 1963; Gillett, 1986). However, green snails are much larger animals than trochus, so that air freight would become very expensive when a large number of adult shells are to be transported. Surface transportation of the snail, keeping them inside baitfish wells, by fishing vessels may be more practical. Of course, this depends on availability of seedstock and a fishing boat for this purpose. Unfortunately, seedstocks are not readily available in the Ryukyus because of widespread over-exploitation of this resource throughout the region.
Even if the above method were practical, and if supplies of seedstock would be found elsewhere, there remains a serious problem of quarantine. Adult shells will require a large space in land-based holding tanks and also consume great quantities of food algae during quarantine period, if such procedures are required. Thus, it is not recommended to transport a large number (hundreds or more) of adult green snail as seedstocks.
The second option is to transport small numbers of adult green snails which will be kept within land-based holding systems. At present, a small facility is available at Lenger Island of Pohnpei Lagoon. This is maintained by the personnel of Pohnpei State Marine Resources Division.
We visited this small hatchery during our survey on Pohnpei. Some giant clams were kept inside several fiberglass tanks which received running sea water. The facility appeared to be adequate for holding a broodstock of green snail to produce juveniles. However, there are some points to be considered as follows.
First of all, there must be at least one full-time aquaculturist who is capable of propagating the snail and who works on site, assisted by supporting staff to maintain the sea water system and other facilities as well as to supply food algae to feed adult and juvenile snails.
The quality of sea water pumped up at the Lenger Hatchery appeared to be good for mariculture of molluscs in general. It is also fortunate that there are abundant algae, such as Laurencia, Hypnea, Eucheuma and perhaps Gracilaria around Pohnpei, good for feeding green snail.
In order to breed green snail at the hatchery, there should be at least 30 adults which are sexed by previous spawning events. Males are easier to induce spawning than females, so that the sex ratio might be arranged as two or three females to one male. This can be done at Akajima Marine Science Laboratory, Establishment of Tropical Marine Ecological Research, if a sufficient fund to cover the operation cost will be made available.
The adult green snails may be transported by the commercial airlines, i.e. Continental Air Micronesia which serves direct flight between Okinawa and Guam and then connecting between Guam and the islands of the FSM. Holding facilities at the Government of Guam/ University of Guam hatchery will become crucial for keeping snails in transit on Guam, if connections were not fast enough between the two flight routes.
The above scheme depends on the availability of a local aquaculturist who will be responsible for the maintenance of broodstock and production of juveniles in the hatchery. On the job training of such a person at the Akajima Lab. and/or Okinawa Fisheries Experimental Station and Government Hatchery in Okinawa will be essential to make himself familiar with the culture system and operation of juvenile production.
There is a need to evaluate, by field experiments, effectiveness of direct larval release for transplantation and ranching of green snail. Competent larvae might be released directly onto the juvenile habitats so that they would settle and grow by themselves. If such a method is feasible, it would certainly reduce the trouble of holding large numbers of juveniles for prolonged periods until their release. On the other hand, this method is also meaningful when there is a surplus of larvae which should be disposed of properly. In fact, fecundity of large green snails is so great (up to 7 million eggs per female) that small hatcheries often may not be able to accommodate the large numbers of embryos and larvae in their facilities.
There remains some uncertainty in reef ranching of such gastropods as green snail and trochus, because their survivorships during nursery phase might not be very high. Laboratories in Okinawa are now working on this problem to identify size-specific mortality and its causes by field experiments.
Dumping large numbers of juveniles in the field should not be carried out before the present study will indicate optimum strategies for releasing juveniles which would result in significant survivorship. Therefore, the third option of direct supply of juveniles from Okinawa is premature at present.
Success of reef ranching of the snails would depend on the continued efforts in basic research to develop a nursery system to improve survivorships of early juveniles. The ocean nursery system for the giant clams is a good example for such purpose. However, an important difference between the clams and the gastropods is that the former live inside the lagoon while the latter are dwellers of the oceanic side of reefs.
It is desired that more research related to this problem will be carried out at as many laboratories as possible, including the MMDC of Palau and Guam hatchery as well as those in FSM and Okinawa. There should be a forum to exchange ideas and information among such laboratories concerned with the problem.
The Guam hatchery is located at an ideal place strategically, because it can produce juveniles of trochus and green snail and distribute them throughout the Micronesian islands using well-established air links. There is no native green snail on Guam, while the population of trochus is established by the past transplantation. Therefore, broodstocks of green snail may be transported from Okinawa to Guam and a cooperative research may be initiated between Univ. of Guam Marine Laboratory and Akajima Marine Science Laboratory.
We discussed this topic with faculty members of the Univ. of Guam during our transits between the FSM and Okinawa. We also visited the Guam hatchery, guided by Dr. Steve Nelson, and were impressed with the facility. It will be much better to supply large numbers of juvenile green snail to the FSM directly from Guam than to transport them from Okinawa via Guam. Dr. Bob Richmond, the Director of the UOG Marine Laboratory and Mr. Barry Smith of the UOG Sea Grant Extension Service both welcomed the idea of cooperative study between the two laboratories.
Transplantation of green snail into the FSM waters may be more practical if a polyculture system will be organized. At present, bivalves such as giant clams and pearl oysters as well as gastropods such as trochus are harvested heavily and widely as commodities of trade and/or subsistence food resources in the FSM and elsewhere in the Pacific.
Gawel (1986) proposed detailed plans for mariculture of various inshore organisms individually. Heslinga (1988) also proposed an implementation plan for the Kosrae Mariculture Center, emphasising cultivation of giant clams.
It is natural to start with an individual species as the target in development of a new project. However, the advantage of polyculture using giant clams and gastropods is obvious because the herbivore gastropods will consume and check overgrowth of algae which is detrimental to growth of the bivalve. The facility of mariculture would be fully utilized if different species were reared sequencially and simultaneously.
Transplantation of exotic organisms might result in disaster because they would not be accepted as new resources in some localities and because they sometimes become pests, contrary to expectations (Eldredge, 1987). Gawel (1988) summarized the past introductions of various organisms into the Pacific. Some of the well-established alien species such as tilapia appear to be unwelcomed at many localities after all.
Introduction of the green snail into the FSM states may be considered as an extension of trochus introduction. The two species were originally distributed within the Indo-Malayan faunal subregion within the Indo-West Pacific, probably because of their poor ability in larval dispersal. They would be accommodated readily in similar habitats and biota of the Indo-Pacific outside the subregion. The past attempts in trochus transplanatation resulted in increased revenues at many Pacific islands and there has been no reported cases of detrimental effects because of its presence.
In order to help familiarize Micronesians with the value of green snail, public education of people in the FSM should be carried out. Shell specimens including a polished shell of green snail have been donated to the Marine Resources Division from the Establishment of Tropical Marine Ecological Research. There is a plan to produce a video presentation featuring biology, utilization, international trade and other aspects of green snail. This would help promote better understanding and support of future programs of its transplantation in the FSM.
Although some of the points have been mentioned in the foregoing sections, we should conclude this report by listing our future targets in our continued research, as follows.
Population parameters such as growth and mortality rates as well as population densities (carrying capacity of habitats) etc. are largely unknown. Also our knowledge on the food and habitat requirements are limited to information from a very limited area (Tokunoshima, in the northern Ryukyus). Therefore, field studies on wild populations of green snail should be carried out at other more central areas of its geographic distribution, such as the waters in Melanesian nations.
The established population by the past transplantation should be studied in detail at Tahiti, in relation to the source (Vanuatu) population, so as to find the reasons of successful transplantation and to detect any adaptational changes in habits and habitats that might have taken place between the two populations.
Careful field studies on mortality rates of released juveniles and their causes should be investigated at the institutions concerned (such as UOG Marine Lab./ Guam Hatchery, Akajima Marine Science Lab. etc.). Likewise, the method of direct larval release should be tested at these institutions.
On the job training of the FSM personnel and exchange of researchers between UOG Marine Lab., MMDC, and AMSL etc. should be programmed and encouraged, during the research and development phase of the green snail transplantation and ranching. External funds from aid agencies such as FAO, SPC, PFDF, CTSA, JICA, and others should be sought after for implementation of this cooperative study.
